Been moved to Support Group after WRAG? No appeal

I am on ESA because of agoraphobia and I recently received a letter about it, with a checkbox ticked stating that I am in the support group, which was news to me as I was put in the WRAG some time last year, didn't bother appealing because I heard how difficult it was, and just left things how they were. Nobody contacted me about any work related activity during that time, however! Then just before Christmas another ESA50 form came through the letterbox so I filled it in and sent it off. and now just a couple of days ago I got this letter saying I am in the support group. I am not complaining, I am just bemused as to why I've been moved over without appealing! I got the follow-up letter today with all the calculations and I am also earning an extra £21.30 from the "Disability Income Guarantee" - What is that? I am not on disability living allowance too, so I hope they have calculated everything correctly and I am actually allowed this because I don't want to claim for something that I'm not allowed.
Any clues as to why I've been moved over (I'm guessing a reassessment happened somewhere along the line without my knowing) and what this DIG thing is?
Thanks!